A magnetic grid is a device for detecting a displacement using electromagnetic characteristic and principles of magnetic recording, and generally includes three parts: a magnet grid ruler, a magnet grid reading head and a detecting circuit. Square wave or sine wave signals recorded by a magnetic head are stored within the magnet grid ruler. When detecting, the magnet grid reading head reads out the square wave or sine wave electromagnetic signals in the magnet grid ruler and converts these signals into electrical signals, and then displacement detection is achieved according to the electrical signals.
In existing magnet grid ruler supporting plate structure for supporting the magnet grid ruler, the supporting plate is generally a long integral strip, wherein the supporting plate is mounted at one side of a machine guide rail pair, and a ruler shell is mounted onto the supporting plate, and magnetic strips are provided within the ruler shell. The magnet grid reading head is mounted at the other side of the machine guide rail pair, and the magnet grid reading head and the magnetic strips are moved relative to each other. Since the magnetic grid belongs to a more precise measuring tool, the gap and parallelism between the magnetic strips and the magnet grid reading head have to be exactly assured in order to make sure measuring precision of the magnet grid. For a long supporting plate in a form of an integral strip, however, its straightness is hard to be assured even though calibration is performed. From a microcosmic view, a long supporting plate is twisted and bent, thus it is difficult to assure straightness of the ruler shell and the magnetic strips, thereby being hard to make sure the magnetic strips are parallel with the magnet grid reading head and then resulting in poor measuring accuracy of the magnet grid.